Bi-aspherical type progressive-power lens

ABSTRACT

To provide a bi-aspherical type progressive-power lens which provides an excellent visual acuity correction for prescription values and a wide effective visual field with less distortion in wearing, by reducing a magnification difference of an image between a distance portion and a near portion. The lens is characterized in that when on a first refractive surface being an object side surface, a surface refractive power in a horizontal direction and a surface refractive power in a vertical direction, at a far vision diopter measurement position F 1 , are DHf and DVf respectively, and on the first refractive surface, a surface refractive power in a horizontal direction and a surface refractive power in a vertical direction, at a near vision diopter measurement position N 1 , are DHn and DVn respectively, relational equations,
 
 DHf+DHn&lt;Dvf+DVn , and  DHn&lt;DVn 
 
are satisfied, and surface astigmatism components at F 1  and N 1  of the first refractive surface are cancelled by the second refractive surface being an eyeball side surface so that the first and second refractive surfaces together provide a far vision diopter (Df) and an addition diopter (ADD) based on prescription values.

TECHNICAL FIELD

The present invention relates to a bi-aspherical type progressive-powerlens, which is a lens used as, for example, a progressive-power lens fora spectacle for presbyopia that is configured to have a progressiverefractive power action dividedly allotted to a first refractive surfacebeing an object side surface and a second refractive surface being aneyeball side surface, so that the first surface and the second surfacetogether provide a far vision diopter (Df) and an addition diopter (ADD)based on prescription values.

BACKGROUND ART

A progressive-power lens is widely used in general because of anadvantage that it is hardly detected from others as a spectacle for theaged in spite of a spectacle lens for presbyopia, an advantage that itallows a wearer to clearly look continuously from a far distance to anear distance without discontinuity, and so on. However, it is alsowidely known that the necessity of arrangement of a plurality of visualfields such as a field for looking far and a field for looking near, andfurther a field for looking at a distance intermediate therebetween,without a boundary line existing within a limited lens area, presentsdisadvantages specific to the progressive-power lens such that eachvisual field is not always sufficiently wide, and that there is a regionmainly in a side visual field which causes the wearer to feel distortionor sway of an image.

Various proposals have been made since long ago to improve thedisadvantages specific to the progressive-power lens, and most of suchconventional progressive-power lenses have a surface configurationcreated by a combination of a “progressive surface” arranged on anobject side surface and a “spherical surface” or a “cylindrical surface”arranged on an eyeball side surface. Conversely to those,Atoral-Variplas as a progressive-power lens, which is characterized inthat a “progressive action” is added to the eyeball side surface, isreleased in 1970 from Essel Optical Co. (now Essilor), France.

Besides, recently proposed prior arts include, for example, technologiesdescribed in Patent International Publication Nos. WO 97/19382 and WO97/19383 and so on, which are generally called rear surface progression(or concave surface progression). The surface configuration in therecently proposed rear surface progression has a main purpose ofimproving distortion and sway of an image by allotting a portion or thewhole of a necessary addition diopter from an object side surface to aneyeball side surface to reduce the magnification difference of an imagebetween a distance portion and a near portion.

Among these prior arts, one described in WO 97/19382 has a configurationin which the object side surface is made a spherical surface or arotationally symmetrical aspherical surface to completely cancel the“progressive action,” and a “progressive surface” providing apredetermined addition diopter is added (fused) to only the eyeball sidesurface. Besides, the prior art described in WO 97/19383 has aconfiguration in which the addition diopter on the “progressive surface”being the object side surface is made lower than a predetermined valueand a “progressive surface” providing a deficiency in addition diopteris added (fused) to a “spherical surface” or “cylindrical surface” onthe rear surface side.

Although having different purposes and reasons, other prior arts of theprogressive-power lens having description of technologies of adding the“progressive action” to the eyeball side surface, include, for example,ones described in Japanese Patent Publication No. Sho 47-23943, JapanesePatent Laid-Open No. Sho 57-10112, Japanese Patent Laid-Open No. Hei10-206805, and Japanese Patent Laid-Open No. 2001-21846. In addition,prior arts in which the “progressive action” is provided to bothsurfaces of a lens, as in one described in the aforementioned WO97/19383, include ones described in Japanese Patent Laid-Open No.2000-338452 and Japanese Patent Laid-Open No. Hei 6-118353. Commonly, inthese prior arts, front and rear two surfaces together provide anecessary addition diopter.

These prior arts have a main purpose of improving distortion and sway ofan image by allotting a portion or the whole of a necessary additiondiopter on an object side surface to an eyeball side surface to reducemagnification difference between a distance portion and a near portion.Clear description, however, on reasons of their improved effects can berarely found, and only partial description thereof is found just in theaforementioned Patent International Publication No. WO 97/19383(hereinafter, Prior art 1) or the like. Namely, Prior art 1 disclosesthe following calculation equations for a lens magnification SM shown inthe equation (1) to the equation (3), the lens magnification SM is usedas a basic evaluation parameter for lens design.

Namely, Prior art 1 includes the following description.

“The lens magnification SM is generally expressed by the followingequation.

 SM=Mp×Ms  (1),

where Mp is called a power factor, and Ms is called a shape factor. Whenthe distance from a vertex of an eyeball side surface (inside vertex) ofa lens to an eyeball is an inter-vertex distance L, a refractive powerat the inside vertex (inside vertex refractive power) is Po, a thicknessat the center of the lens is t, a refractive index of the lens is n, anda base curve (refractive power) of the object side surface of the lensis Pb, Mp and Ms are expressed as follows.Mp=1/(1−L×Po)  (2)Ms=1/(1−(t×Pb)/n)  (3)It should be noted that for calculations of the equation (2) and theequation (3), dioptry (D) is used for the inside vertex refractive powerPo and the base curve Pb, and meter (m) is used for the distance L andthickness t, respectively.”

Then, these calculation equations for the lens magnification SM are usedto calculate a difference in magnification between a distance portionand a near portion. In Prior art 1, it is regarded that the distortionand sway of an image are improved because of a small magnificationdifference.

The study by the inventor of the invention shows that though someeffects are recognized in the above-described Prior art 1 as compared toits prior art, the following points need to be discussed to design alens with higher performance.

-   a. Basic evaluation parameters used in the above-described Prior art    1 include a parameter which should be essentially applied only to a    portion near the center of a lens as is clear from the description    of “the distance L from a vertex of an eyeball side surface of a    lens to an eyeball” and “a thickness t at the center of the lens.”    More specifically, in an example of Prior art 1, the basic    evaluation parameter to be applied only to a distance portion near    the center of the lens, is applied also to a near portion positioned    at a great distance below the lens center, thus presenting a    possibility of error.-   b. In Prior art 1, the lens magnification SM is calculated using    five basic evaluation parameters, composed of the aforementioned    ones with addition of the “refractive index of the lens n.” However,    as is instantly found when tilting forward and backward a lens    having an actual diopter, it is considered that the size of an image    is strongly influenced by an “angle between a sight line and a lens    surface.” This leads to a consideration that the “angle between a    sight line and a lens surface” is nonnegligible particularly in    calculation of the magnification of the near portion positioned at a    great distance below the lens center. Accordingly, the lens design    of Prior art 1 has a possibility of error caused by the “calculation    of the lens magnification without consideration of the angle between    a sight line and a lens surface.”-   c. Prior art 1 only describes the “magnification” for an application    example to a cylindrical lens but lacks idea on direction thereof,    which causes a possibility of error when “magnifications in the    vertical direction and the horizontal direction are different” which    occurs, for example, in the near portion positioned at a great    distance below the lens center.-   d. To accurately calculate the magnification for the near portion,    the distance to a visual target, that is, an “object distance”    should be added as a calculation factor. In Prior art 1, the “object    distance” is not taken into consideration, which presents an    undeniable possibility of error.-   e. In the magnification calculations, the influence by a prism    action is not taken into consideration, which may cause an error.

As described above, the prior art may not be always sufficient from aviewpoint, in particular, of more accurately calculating the“magnification.”

The present invention is made to solve the above problems, and itsobject is to provide a bi-aspherical type progressive-power lens whichprovides an excellent visual acuity correction for prescription valuesand a wide effective visual field with less distortion in wearing, byreducing a magnification difference of an image between a distanceportion and a near portion through correct calculation of themagnification of the image with an influence by an “angle between asight line and a lens surface” and an “object distance” taken intoconsideration.

It is another object of the present invention to provide a bi-asphericaltype progressive-power lens which makes it possible to use a“bilaterally symmetrical semifinished product” as an object side surfaceand process after acceptance of an order only an eyeball side surfaceinto a bilaterally asymmetrical curved surface coping with a convergenceaction of an eye in near vision, and to reduce processing time and cost.

DISCLOSURE OF THE INVENTION

As means to solve the above-described problems, in a first means,

in a bi-aspherical type progressive-power lens with a progressiverefractive power action dividedly allotted to a first refractive surfacebeing an object side surface and a second refractive surface being aneyeball side surface,

when on the first refractive surface, a surface refractive power in ahorizontal direction and a surface refractive power in a verticaldirection, at a far vision diopter measurement position F1, are DHf andDVf respectively, and

on the first refractive surface, a surface refractive power in ahorizontal direction and a surface refractive power in a verticaldirection, at a near vision diopter measurement position N1, are DHn andDVn respectively, relational equations,DHf+DHn<Dvf+DVn, and DHn<DVnare satisfied, and surface astigmatism components at F1 and N1 of thefirst refractive surface are cancelled by the second refractive surfaceso that the first and second refractive surfaces together provide a farvision diopter (Df) and an addition diopter (ADD) based on prescriptionvalues.

In a second means,

in the bi-aspherical type progressive-power lens according to the firstmeans, relational equations DVn−DVf>ADD/2, and DHn−DHf<ADD/2 aresatisfied.

In a third means,

in the bi-aspherical type progressive-power lens according to the firstor second means, the first refractive surface is bilaterally symmetricalwith respect to one meridian passing through the far vision dioptermeasurement position F1, the second refractive surface is bilaterallyasymmetrical with respect to one meridian passing through a far visiondiopter measurement position F2 of the second refractive surface, and aposition of a near vision diopter measurement position N2 on the secondrefractive surface is shifted inward to a nose by a predetermineddistance.

In a fourth means,

in the bi-aspherical type progressive-power lens according to any one ofthe first to the third means, the first refractive surface is a rotationsurface with as a generatrix one meridian passing through the far visiondiopter measurement position F1, the second refractive surface isbilaterally asymmetrical with respect to one meridian passing through afar vision diopter measurement position F2 on the second refractivesurface, and a position of a near vision diopter measurement position N2on the second refractive surface is shifted inward to a nose by apredetermined distance.

The above-described means are devised based on the following results ofclarification. Hereinafter, description will be made with reference tothe drawings. FIG. 1 is an explanatory view of various surfacerefractive powers at positions on a spectacle lens surface, FIG. 2 is anexplanatory view of a positional relation among an eyeball, sight lines,and a lens, FIG. 3-1, FIG. 3-2, and FIG. 3-3 and FIG. 4-1, FIG. 4-2, andFIG. 4-3 are explanatory views on a magnification M γ of a prism, beingexplanatory views on a difference between a plus lens and a minus lensand on a difference in magnification in viewing mainly using a nearportion which is a lower portion of a lens, FIG. 5-1 is an explanatoryview of an optical layout of progressive-power lens, being a front viewof the progressive power lens when viewed from an object side surface,FIG. 5-2 is an explanatory view of the optical layout of theprogressive-power lens, being a side view illustrating a cross sectionin the vertical direction, FIG. 5-3 is an explanatory view of theoptical layout of the progressive-power lens, being an elevational viewillustrating a cross section in the transverse direction, and FIG. 6 isan explanatory view illustrating the difference of definition on“addition diopter.” Note that in these drawings, symbol F denotes a farvision diopter measurement position, symbol N denotes a near visiondiopter measurement position, and symbol Q denotes a prism dioptermeasurement position. In addition, other symbols shown in FIG. 1 and soon denote,

DVf: surface refractive power at F of a sectional curved line in thevertical direction passing through F,

DVn: surface refractive power at N of a sectional curved line in thevertical direction passing through N,

DHf: surface refractive power at F of a sectional curved line in thehorizontal direction passing through F, and

DHn: surface refractive power at N of a sectional curved line in thehorizontal direction passing through N. Further, suffix 1 is added toall of the symbols when the refractive surface of a drawing is a firstrefractive surface being the object side surface, and suffix 2 is addedto all of the symbols when the surface is a second refractive surfacebeing the eyeball side surface for recognition.

Besides, symbols F1 and F2 denote far vision diopter measurementpositions on the object side surface and the eyeball side surface, andsimilarly symbols N1 and N2 denote near vision diopter measurementpositions on the object side surface and the eyeball side surface.Further, symbol E is an eyeball, symbol C a center of rotation of theeyeball, symbol S a reference surface around C, symbols Lf and Ln sightlines passing through the far vision diopter measurement position andnear vision diopter measurement position respectively. Besides, symbol Mis a curved line called a main gazing line through which a sight linepasses when one looks with both eyes from an upper front to a lowerfront portion. Then, symbols F1, N1, F2, N2, and N3 indicate positions,to which an opening of a lens meter is placed, differing depending onthe definition of the “addition diopter.”

First, a calculation equation of a magnification corresponding to thenear vision improved by “corresponding parameters to the near portion”which is the problem (a) of the above-described prior art and“considering the object distance” which is the problem (d), was designedto be obtained as follows. Namely, when Mp is a power factor and Ms is ashape factor, a magnification SM of an image is expressed bySM=Mp×Ms  (1′).Here, when the objective power (inverse number of the object distanceexpressed in a unit of m) to a visual target is Px, the distance fromthe eyeball side surface in the near portion of the lens to the eyeballis L, the refractive power in the near portion (inside vertex refractivepower in the near portion) is Po, the thickness in the near portion ofthe lens is t, the refractive index of the lens is n, and the base curve(refractive power) of the object side surface in the near portion of thelens is Pb, the following relation is established.Mp=(1−(L+t)Px)/(1−L×Po)  (2′)Ms=1/(1−t×(Px+Pb)/n)  (3′)

These equations, in which the parameters are made to correspond to thedistance portion, and 0 corresponding to infinity is substituted for Pxindicating power of the object distance, match the equations of theabove-described Prior art 1. In other words, the equations used in Priorart 1 can be considered to be equations dedicated for the far visionhaving an infinitive object distance. By the way, although the equation(1′) here is identical to the equation of the above-described Prior art1, the object distance in near vision is generally about 0.3 m to about0.4 m, and thus Px which is the inverse number thereof becomes a valuefrom about −2.5 to about −3.0. Accordingly, Mp increases in the equation(2′) because the numerator increases, and Ms decreases in the equation(3′) because the denominator increases. This shows that the influence bythe shape factor Ms in the near vision is less than that by thecalculations of Prior art 1. For example, when Pb=−Px, that is, the basecurve (refractive power) of the surface on the object side of a lens hasa value ranging from about +2.5 to about +3.0, Ms=1, which shows thatthe shape factor in the near vision is completely irrelevant to themagnification of an image.

Although, in the above-described manner, the calculation equations formagnification with the parameters corresponding to the near portion andthe “object distance” taken into consideration have been obtained, the“angle between a sight line and a lens surface” which is the problem (b)of the above-described Prior art 1 also needs to be taken intoconsideration to calculate a magnification in actual near vision. Whatis an important here is that the “angle between a sight line and a lenssurface” has a directional property. In other words, taking the “anglebetween a sight line and a lens surface” into consideration is nothingbut concurrently taking into consideration the directional property ofthe “magnification of an image” which is the problem (c) of theabove-described Prior art 1.

Reviewing the first calculation equation of the above-describedequations (1′) to (3′) in this viewpoint, it has as calculation factorsinfluenced by the “angle between a sight line and a lens surface,” theinside vertex refractive power Po in the near portion and the base curve(refractive power) Pb of the object side surface in the near portion.Here, when well-known Martin's approximate equations are used, with theangle formed between the sight line in near vision and the optical axisof the region in the near portion being α and the angle formed betweenthe sight line in the near vision and the normal line on the object sidesurface in the near portion being β,

the inside vertex refractive power in the vertical direction in the nearportion:Pov=Po×(1+Sin² α×4/3),the inside vertex refractive power in the horizontal direction in thenear portion:Poh=Po×(1+Sin² α×1/3),the vertical section refractive power on the object side surface in thenear portion:Pbv=Pb×(1+Sin² β×4/3), andthe transverse section refractive power on the object side surface inthe near portion:Pbh=Pb×(1+Sin² β×1/3).As long as the angles α and β and Po and Pb are not zero, the refractivepowers, power factors, and shape factors have different values betweenthe vertical and horizontal directions as described above, resulting ina difference in magnification occurring between the vertical directionand the horizontal direction.

By the way, while the approximate equations are used here to explainsimply a fact that “the refractive power varies depending on thedirection of the sight line,” these values are desirably obtained byaccurate ray tracing calculation in the actual optical design. In anonattributive example of the method of calculating these, for example,an optical path along the sight line is calculated using Snell's law tocalculate L, t, and the distance from the object side refractive surfaceto an object point, and then, along-this optical path, the firstfundamental form, the second fundamental form, Weingarten formula, orthe like in differential geometry can be used to calculate therefractive power with the influence of refraction on the optical path onthe object side refractive surface and the eyeball side refractivesurface taken into consideration. These equations and formula andcalculating methods are known from long ago and described in a knownliterature “Differential Geometry” (written by Kentaro Yano, publishedby Asakura Shoten Kabusikikaisya, the first edition, 1949) and so on,and thus the description thereof is omitted.

By the way, by performing such accurate ray tracing calculations, fourcalculation factors L, Po, t, and Pb which are the above-describedproblems (a) to (d) are taken into consideration, and accuratemagnification calculations can be possible in all of sight linedirections as well as in the near portion located at a great distancebelow the lens center. In such a manner, the above-described items,

the inside vertex refractive power in the vertical direction in the nearportion: Pov,

the inside vertex refractive power in the horizontal direction in thenear portion: Poh,

the vertical section refractive power on the object side surface in thenear portion: Pbv, and

the transverse section refractive power on the object side surface inthe near portion: Pbh,

can be obtained at an accuracy higher than that in a case using Martin'sapproximate equations.

It will be easily understood that all of the above-describedmagnification calculations of an image have to correspond to thedifference in the direction of the sight line from the fact that the“the refractive power varies in accordance with the direction of thesight line,” as described above. Here, when Mp is the power factor andMs is the shape factor, and suffix v is added for the vertical directionand suffix h is added for the horizontal direction to express themagnification SM of an image, the above-described equations (1′) to (3′)are rewritten as follows:SMv=Mpv×Msv  (1v′)SMh=Mph×Msh  (1h′)Mpv=(1−(L+t)Px)/(1−L×Pov)  (2v′)Mph=(1−(L+t)Px)/(1−L×Poh)  (2h)Msv=1/(1−t×(Px+Pbv)/n)  (3v′)Msh=1/(1−t×(Px+Pbh)/n)  (3h′).

The above way could cope with the above-described problems (a) to (d) ofPrior art 1. At last, the “influence by the prism action” which is theabove-described problem (e) in calculating the magnification in theactual near vision will be described. While a prism itself has norefractive power unlike a lens, the magnification M γ of the prismvaries depending on the incident angle and exit angle of rays to/fromthe prism. Here, an angle magnification γ when a ray incident from avacuum to a medium with a refractive index n, as shown on the left sidein FIG. 3-1 and FIG. 4-1, is refracted on the surface of the medium isconsidered. When the incident angle is i and the refractive angle is rin this event, n=Sin i/Sin r by well-known Snell's law. Besides, theangle magnification γ by refraction is expressed by γ=Cos i/Cos r. Sincen≧1, generally i≧r and γ≦1. Here, γ becomes a maximum value 1 wheni=r=0, that is, in the case of a normal incidence. When the refractiveangle r is as n=1/Sin r, γ becomes a theoretical minimum value, γ=0. Atthis time, i=π/2, and thus r is equal to a critical angle of totalreflection when a ray exits from the medium.

On the other hand, an angle magnification γ′ when a ray exits from amedium with a refractive index of n to a vacuum, as shown on the rightside in FIG. 3-1 and FIG. 4-1, becomes completely reverse to the above.More specifically, when the incident angle of a ray, which is refractedon a medium surface and exits from within the medium to a vacuum, is i′and the refractive angle is r′, 1/n=Sin i′/Sin r′ by Snell's law, andthe angle magnification is expressed by γ′=Cos i′/Cos r′. Since n≧1,generally r′≧i′ and γ′≧1. Here, γ′ becomes a maximum value 1 wheni′=r′=0, that is, in the case of a normal incidence. When the incidentangle i′ is as n=1/Sin i′, γ′ becomes a theoretical maximum value, γ′=∞.At this time, r′=π/2, and thus i′ is equal to a critical angle of totalreflection when a ray exits from the medium.

As shown in FIG. 3-3 and FIG. 4-3, a case in which a ray incident on theobject side surface of one spectacle lens passes through the inside ofthe lens, exits from the eyeball side surface, and reaches an eyeball,is considered (hereinafter, it should be conveniently considered thatthe refractive index of air is approximated to be 1 that is the same asin a vacuum to simplify description). When the refractive index of aspectacle lens is n, the incident angle of a ray incident on the objectside surface is i, the refractive angle is r, the incident angle of aray from within the lens reaching the eyeball side surface is i′, andthe refractive angle of an emergent ray is r′, the angle magnificationMγ passing through the two surfaces of the spectacle lens is expressedby a product of the above-described two kinds of angle magnifications,Mγ=γ×γ′=(Cos i×Cos i′)/(Cos r×Cos r′).This is irrelevant to the refractive power on the lens surface and knownas a magnification of a prism.

Here, when a case of i=r′ and r=i′ as shown in FIG. 3-1 and FIG. 4-1 isconsidered,Mγ=γ×γ′=1,which means that there is no change in magnification of an image seenthrough a prism. Meanwhile, when a ray is perpendicularly incident onthe object side surface of the spectacle lens as shown in FIG. 3-2,Mγ=γ′=Cos i′/Cos r′≧1,and conversely, when a ray perpendicularly exits from the eyeball sidesurface of the spectacle lens as shown in FIG. 4-2,Mγ=γ=Cos i/Cos r≦1.

Here, what is important is that the magnifications Mγ of a prism have adirectional property. More specifically, when the distribution of prismsin a progressive-power lens is considered, it naturally varies dependingon the diopter and prescription prism value, in which generally prismsin the far vision near the lens center are small and prisms in thevertical direction in the near vision located at a lower portion of thelens are large. Therefore, it can be said that the magnification Mγ ofthe prism has great influence especially on the vertical direction inthe near vision.

Not only a progressive-power lens, but also a typical spectacle lens hasa meniscus shape in which the object side surface is convex and theeyeball side surface is concave, and thus taking it into considerationthat the sight line in near vision is in a downward direction, it can besaid that the near vision through the progressive-power lens having apositive refractive power in the near portion as shown in FIG. 3-3, issimilar to the shape in FIG. 3-2 of Mγ≧1 rather than in FIG. 3-1 ofMγ=1, and at least Mγ>1. Similarly, it can be said that the near visionthrough the progressive-power lens having a negative refractive power inthe near portion as shown in FIG. 4-3, is similar to the shape in FIG.4-2 of Mγ≦1 rather than in FIG. 4-1 of Mγ=1, and at least Mγ<1.Accordingly, Mγ>1 in the near vision through the progressive-power lenshaving a positive refractive power in the near portion, and Mγ<1 in thenear vision through the progressive-power lens having a negativerefractive power in the near portion.

While the magnification SM of the lens in Prior art 1 is grasped only asa product of the power factor Mp and the shape factor Ms as describedabove, the present invention aims to further multiply the product by themagnification M γ of a prism to obtain a correct magnification of alens.

The magnification M γ by a prism is called a “prism factor” in contrastwith Mp and Ms, and when suffix v is added for the vertical direction,and suffix h is added for the horizontal direction to express themagnification SM of an image, the above-described equations (1v′) and(1h′) are rewritten as follows:SMv=Mpv×Msv×Mγv  (1v″)SMh=Mph×Msh×Mγh  (1h″).It should be noted that these M γ v and M γ h can be obtained in theprocess of the above-described accurate ray tracing calculations. Thiscan solve the problem of the influence by the prism action in themagnification calculations of a spectacle.

In a typical convex surface progressive-power lens, the distance portionis lower than the near portion in surface refractive power of a“progressive surface” being the object side surface. In contrast tothis, in the progressive-power lens of Prior art 1, the distance portionis set equal to the near portion in surface refractive power of a“progressive surface” being the object side surface, thereby changingthe ratio in the shape factor between the distance and near portions anddecreasing the magnification difference between the distance and nearportions, so as to improve the distortion and sway of an image by theprogressive-power lens. In the study in the present invention, however,it is shown that although a reduction in the surface refractive powerdifference between the distance and near portions of a “progressivesurface” being the object side surface presents an advantage of adecrease in the magnification difference of an image between thedistance and near portions in the horizontal direction, there are someproblems in decreasing the surface refractive power difference in thevertical direction.

A first problem is influence by the prism factor M γ v in the verticaldirection. The prism factor M γ v in the vertical direction is as M γv<1 when the near portion has a negative refractive power, and M γ v>1when the near portion has a positive refractive power as describedabove, and this tendency is enhanced by decreasing the surfacerefractive power difference in the vertical direction, whereby M γ vdeviates from M γ v=1, which is a magnification of a naked eye, ineither case of the diopter in the near portion being positive ornegative. Meanwhile, the prism factor M γ h in the horizontal directionreceives no such influence, and thus it is kept as M γ h=1. As a result,there arises a difference between the vertical and horizontal directionsin the magnification of an image especially in a portion from the nearportion to a portion lower than that, thereby causing a disadvantagethat an item which should look square under proper condition lookslonger than wider in a plus diopter and wider than longer in a minusdiopter.

A second problem is one occurring only when the near portion has apositive refractive power especially in the vertical direction.Specifically, when the surface refractive power difference in thevertical direction is decreased, the angle between the sight line andthe lens surface in the near vision is further increased, whereby thepower factor Mpv in the vertical direction is increased and acts doublywith the increase in the prism factor M γ v in the vertical direction,which is the first problem, to increase the magnification SMv in thevertical direction, resulting in a disadvantage that the magnificationdifference of an image between the distance and near portions increases.

In short, it is shown that the reduction in the surface refractive powerdifference between the distance and near portions of a progressivesurface being the object side surface is an advantage in the horizontaldirection but is conversely deterioration in the vertical direction.Therefore, in a conventional-type convex surface progressive-power lens,the above-described problems can be solved by dividing the progressivesurface being the object side surface into the vertical direction andthe horizontal direction, and decreasing the surface refractive powerdifference between the distance and near portions only in the horizontaldirection.

These things completely apply to the fact that “the visual field iswidened” which is generally regarded as a merit of rear surfaceprogression (or concave surface progression) as described below.

It is generally known that an excellent visual field in the horizontaldirection has its limits since there is astigmatism in the peripheralportion of the “progressive surface,” but if the “progressive surface”is placed on the eyeball side surface, the “progressive surface” itselfapproaches the eye to present an advantage that the excellent visualfiled is widened in the horizontal direction. On the other hand, thisresults in a further distance between the distance and near visualregions in the vertical direction to present a disadvantage that a laborincreases in rotating the eye from the far vision to the near vision. Inother words, the rear surface progression (or concave surfaceprogression), as compared to the conventional front surface progression(or convex surface progression), presents an advantage of widening thevisual field in the horizontal direction but a disadvantage ofincreasing the rotating angle of the eye from the far vision to the nearvision in the vertical direction.

The present invention, however, includes the progressive refractingsurface which satisfies the relational equations DHf+DHn<DVf+DVn andDHn<DVn, or DVn−DVf>ADD/2 and DHn−DHf<ADD/2 as described above, and thusthe present invention has characteristics created by the rear surfaceprogression (or concave surface progression) greater than those by theconventional front surface progression (or convex surface progression)in the horizontal direction, and characteristics created by theconventional front surface progression (or convex surface progression)greater than those by the rear surface progression (or concave surfaceprogression) in the vertical direction. Therefore, according to thepresent invention, it is possible to restrain the disadvantage ofincreasing the eyeball rotating angle between the distance and nearportions in the vertical direction while receiving the advantage ofincreasing the visual field in the horizontal direction.

Further, in an extreme example within the scope of the presentinvention, when DVn−DVf=ADD and DHn−DHf=0, a lens has progressionsidentical to the conventional front surface progression (or convexsurface progression) in the vertical direction and to the rear surfaceprogression (or concave surface progression) in the horizontaldirection. Therefore, this case presents an extremely excellent resultthat the advantage in the horizontal direction can be obtained withoutthe disadvantage in the vertical direction.

Further, these things also apply to decreasing the magnificationdifference of an image between the distance portion and the near portionand improving the distortion and sway of the image as described above,and thus they can be advantages of the present invention.

As has been described, the most important characteristic of the presentinvention is that a progressive action of a progressive-power lens isdivided in the vertical direction and the horizontal direction of thelens, and then an optimal sharing ratio between the front and rear twosurfaces is set in each direction to configure one bi-aspherical typeprogressive-power lens. As an extreme example, it is also within thescope of the present invention that all the progressive action in thevertical direction is provided by the object side surface, and all theprogressive action in the horizontal direction is provided by theeyeball side surface. In this case, since either of the front and reartwo faces does not function as a normal progressive surface only by onesurface, the addition diopter as a progressive surface cannot bespecified. This results in a progressive-power lens having the front andrear surfaces both of which are not progressive surfaces. Contrarily,although the above-described various prior arts are different in sharingratio, in any of them the “value” of a required addition diopter isallotted to front and rear two surfaces, and after an actual progressivesurface to which each allotted addition diopter is given is imagined, acombined surface with a cylindrical surface is configured as required.Consequently, the point of the preset invention definitely differentfrom the prior arts exists in the configuration of a bi-aspherical typeprogressive-power lens using, on both surfaces, aspherical surfaceshaving progressive actions different depending on direction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory view of various surface refractive powers atpositions on a spectacle lens;

FIG. 2 is an explanatory view of a positional relation among an eyeball,sight lines, and a lens surface;

FIG. 3-1 is an explanatory view on a magnification M γ of a prism, beingan explanatory view on a difference between a plus lens and a minus lensand on a difference in magnification in viewing mainly using a nearportion which is a lower portion of a lens;

FIG. 3-2 is an explanatory view on a magnification M γ of a prism, beingan explanatory view on a difference between a plus lens and a minus lensand on a difference in magnification in viewing mainly using a nearportion which is a lower portion of a lens;

FIG. 3-3 is an explanatory view on a magnification M γ of a prism, beingan explanatory view on a difference between a plus lens and a minus lensand on a difference in magnification in viewing mainly using a nearportion which is a lower portion of a lens;

FIG. 4-1 is an explanatory view on a magnification M γ of a prism, beingany explanatory view on a difference between a plus lens and aminus-lens and on a difference in magnifications in viewing mainly usinga near portion which is a lower portion of a lens;

FIG. 4-2 is an explanatory view on a magnification M γ of a prism, beingan explanatory view on a difference between a plus lens and a minus lensand on a difference in magnifications in viewing mainly using a nearportion which is a lower portion of a lens;

FIG. 4-3 is an explanatory view on a magnification M γ of a prism, beingan explanatory view on a difference between a plus lens and a minus lensand on a difference in magnifications in viewing mainly using a nearportion which is a lower portion of a lens;

FIG. 5-1 is an explanatory view of an optical layout of aprogressive-power lens, being a front view of the progressive power lenswhen viewed from an object side surface;

FIG. 5-2 is an explanatory view of the optical layout of theprogressive-power lens, being a side view illustrating a cross sectionin the vertical direction;

FIG. 5-3 is an explanatory view of the optical layout of theprogressive-power lens, being an elevational view illustrating a crosssection in the transverse direction;

FIG. 6 is an explanatory view illustrating the difference of definitionon “addition diopter”;

FIG. 7 is a view collectively showing in Table 1-1 and Table 1-2“surface refractive powers” and “results of accurate magnificationcalculations in a direction of a specific sight line” of Examples 1, 4,5, and 6 and Prior arts A, B, and C corresponding to the diopters ofExamples 1, 4, 5, and 6;

FIG. 8 is a view collectively showing in Table 2-1 and Table 2-2“surface refractive powers” and “results of accurate magnificationcalculations in a direction of a specific sight line” of Examples 2 and7 and Prior arts A, B, and C corresponding to the diopters of Examples 2and 7;

FIG. 9 is a view collectively showing in Table 3-1 and Table 3-2“surface refractive powers” and “results of accurate magnificationcalculations in a direction of a specific sight line” of Example 3 andPrior arts A, B, and C corresponding to the diopters of the example 3;

FIG. 10 is a view showing Graphs 1-1, 1-2, 2-1, and 2-2 representing thesurface refractive power distributions of Example 1 and Example 2;

FIG. 11 is a view showing Graphs 3-1 and 3-2 representing the surfacerefractive power distributions of Example 3;

FIG. 12 is a view showing Graphs 4-1, 4-2, 5-1, 5-2, 6-1 and 6-2representing the surface refractive power distributions of Example 4 toExample 6;

FIG. 13 is a view showing Graphs 7-1 and 7-2 representing the surfacerefractive power distributions of Example 7;

FIG. 14 is a view showing Graphs A-1, A-2, B-1, B-2, C-1 and C-2representing the surface refractive power distributions of Prior artexamples A, B, and C;

FIG. 15 is a view showing Graph 1-3-Msv representing results, obtainedby performing accurate magnification calculations, of magnificationdistributions when lenses of Example 1 and three kinds of Prior artexamples A, B, and C corresponding to the diopters of Example 1 areviewed along main gazing lines;

FIG. 16 is a view showing Graph 1-3-Msh representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 1 areviewed along the main gazing lines;

FIG. 17 is a view showing Graph 1-3-Mpv representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 1 areviewed along the main gazing lines;

FIG. 18 is a view showing Graph 1-3-Mph representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 1 areviewed along the main gazing lines;

FIG. 19 is a view showing Graph 1-3-M γ v representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopter of Example 1 areviewed along the main gazing lines;

FIG. 20 is a view showing Graph 1-3-M γ h representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 1 areviewed along the main gazing lines;

FIG. 21 is a view showing Graph 1-3-SMv representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 1 areviewed along the main gazing lines;

FIG. 22 is a view showing Graph 1-3-SMh representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 1 areviewed along the main gazing lines;

FIG. 23 is a view showing Graph 2-3-Msv representing results, obtainedby performing accurate magnification calculations, of magnificationdistributions when lenses of Example 2 and three kinds of Prior artexamples A, B, and C corresponding to the diopters of Example 2 areviewed along main gazing lines;

FIG. 24 is a view showing Graph 2-3-Msh representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines;

FIG. 25 is a view showing Graph 2-3-Mpv representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines;

FIG. 26 is a view showing Graph 2-3-Mph representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines;

FIG. 27 is a view showing Graph 2-3-M γ v representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines;

FIG. 28 is a view showing Graph 2-3-M γ h representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines;

FIG. 29 is a view showing Graph 2-3-SMv representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines;

FIG. 30 is a view showing Graph 2-3-SMh representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines;

FIG. 31 is a view showing Graph 3-3-Msv representing results, obtainedby performing accurate magnification calculations, of magnificationdistributions when lenses of Example 3 and three kinds of Prior artexamples A, B, and C corresponding to the diopters of Example 3 areviewed along main gazing lines;

FIG. 32 is a view showing Graph 3-3-Msh representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines;

FIG. 33 is a view showing Graph 3-3-Mpv representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines;

FIG. 34 is a view showing Graph 3-3-Mph representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines;

FIG. 35 is a view showing Graph 3-3-M γ v representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines;

FIG. 36 is a view showing Graph 3-3-M γ h representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines;

FIG. 37 is a view showing Graph 3-3-SMv representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines; and

FIG. 38 is a view showing Graph 3-3-SMh representing results, obtainedby performing accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a bi-aspherical type progressive-power lens according to anembodiment of the present invention of the application will bedescribed. In the following description, a designing method used forobtaining the bi-aspherical type progressive-power lens according to theembodiment will be described first, and then the bi-aspherical typeprogressive-power lens according to the embodiment will be described.

(Procedures of Lens Design)

The outline of procedures of an optical designing method of thebi-aspherical type progressive-power lens according to the embodiment isas follows:

-   {circle around (1)} Setting of input information,-   {circle around (2)} Double surface design as a convex    progressive-power lens,-   {circle around (3)} Conversion into a convex surface shape of the    present invention and accompanying rear surface correction, and-   {circle around (4)} Rear surface correction accompanying a    transmission design, a Listing's law-compliant design, and so on.    Hereinafter, the individual procedure will be made into further    divided steps for detailed description.    {circle around (1)} Setting of Input Information

The input information is roughly divided into the following two kinds(information other than optical design is omitted).

{circle around (1)}-1: Item Specific Information

Data specific to a lens item. A refractive index of a raw material Ne, aminimum center thickness CTmin, a minimum edge thickness ETmin,progressive surface design parameters, and so on.

{circle around (1)}-2: Wearer Specific Information

A far vision diopter (a spherical surface diopter S, a cylindricaldiopter C, a cylindrical axis AX, a prism diopter P, a prism basedirection PAX, and so on), an addition diopter ADD, frame shape data(preferably, three-dimensional shape data), frame wearing data (aforward tilt angle, a horizontal tilt angle, and so on), an inter-vertexdistance, lay-out data (a far vision PD, a near vision CD, an eye pointposition, and so on), and other data on an eyeball. It should be notedthat progressive surface design parameters such as a progressive zonelength specified by a wearer, a measuring method of an addition diopter,an amount of inner shift of the near portion are classified into thewearer specific information.

{circle around (2)} Double Surface Design as a Convex Progressive-PowerLens

A lens is first designed, divided into a convex surface and a concavesurface, as a conventional type convex progressive-power lens.

{circle around (2)}-1: Convex Surface Shape (Convex Progressive Surface)Design

To realize the addition diopter ADD and the progressive zone lengthprovided as input information, a conventional type convex progressivesurface shape is designed in accordance with the progressive surfacedesign parameters being the input information. Various conventionalknown technologies can be used in the design in this step, and thus thedesign technology of the present invention is unnecessary.

A specific example of this method is, for example, a method of settingfirst a “main meridian” corresponding to a spine when forming a lenssurface. It is preferable that the “main meridian” is finally a “maingazing line” corresponding to an intersecting line of a sight line and alens surface when a spectacle wearer looks with both eyes from a frontupper portion (far) to a lower portion (near). However, the inner shiftof the near region in response to the convergence action of the eye inthe near vision is not necessarily dealt with through inner shift of the“main gazing line” as will be described later. Therefore, the “maingazing line” here is defined as one meridian (main meridian) in thevertical direction which passes through the lens center and divides thelens surface into a right part and a left part. A lens has front andrear two surfaces, and thus there are two “main meridians” on the frontand rear surfaces. The “main meridian” looks straight when viewedperpendicularly to the lens surface, but it generally becomes a curvedline in a three-dimensional space when the lens surface is a curvedsurface.

Then, based on the information such as a predetermined addition diopterand progressive zone length, an appropriate refractive powerdistribution along the “main meridian” is set. Although the refractivepower distribution can be set dividedly to the front and rear twosurfaces, with the influence by the thickness of the lens and an anglebetween a sight line and a refractive surface taken into consideration,all the progressive action should be provided on a first refractivesurface being an object side surface since the conventional type convexprogressive surface shape is designed in this step. Therefore, forexample, assuming that when a surface refractive power of a frontsurface (a first refractive surface being an object side surface) of alens is D1, and a surface refractive power of a rear surface (a secondrefractive surface being an eyeball side surface) of the lens is D2, aresulting transmission refractive power is D, generally the transmissionrefractive power D can be approximately obtained as D≈D1−D2. Thecombination of D1 and D2, however, preferably has a meniscus shape inwhich the object side surface is convex and the eyeball side surface isconcave. Note that D2 has a positive value here. Although the rearsurface of the lens is generally a concave surface and thus has asurface refractive power of a negative value, D2 should be given apositive value in this specification for simplification of descriptionto calculate the transmission refractive power D by subtracting D2 fromD1.

A relational equation between the surface refractive power and thesurface shape is generally defined by the following equation,Dn=(N−1)/Rwhere Dn: a surface refractive power of an n-th surface (unit: diopter),N: a refractive index of a lens material, R: a radius of curvature(unit: m). Therefore, a method of converting the distribution of thesurface refractive power into a distribution of curvature uses theequation,1/R=Dn/(N−1),created by transforming the above relational equation. By obtaining thedistribution of curvature, the geometrical shape of the “main meridian”is uniquely determined, which means that the “main meridian”corresponding to the spine in forming a lens surface is set.

What is required next is a “sectional curved line group in thehorizontal direction” corresponding to costae in forming the lenssurface. Though intersecting angles of the “sectional curved line groupin the horizontal direction” and the “main meridian” are not necessarilyright angles, each “sectional curved line in the horizontal direction”should intersect at right angles with the “main meridian” to simplifythe description Further, “surface refractive powers in the horizontaldirection” of the “sectional curved line group in the horizontaldirection” at intersections with the “main meridian” do not always needto be identical to “surface refractive powers in the vertical direction”along the “main meridian”, and the present invention is made based onthe difference in the surface refractive power between the verticaldirection and the horizontal direction as actually described in claims.In the design in this step, however, since the conventional type convexprogressive surface shape is designed, the surface refractive powers inthe vertical direction and the horizontal direction at the intersectionsshould be identical with each other.

By the way, all the “sectional curved lines in the horizontal direction”can be simple circular curved lines having surface refractive powers atthe intersections, and can also be made with applications by variousprior arts incorporated thereto. One of conventional technologies onsurface refractive power distribution along the “sectional curved linein the horizontal direction” is, for example, a technology in JapanesePatent Publication No. Sho 49-3595. This technology is characterized inthat one “sectional curved lines in the horizontal direction” in analmost circular shape is set near the center of a lens, and sectionalcurved lines positioned at an upper portion is made to have adistribution of surface refractive power increasing from the center tothe side, and sectional curved lines positioned at a lower portion ismade to have a distribution of surface refractive power decreasing fromthe center to the side. As described above, the “main meridian” and the“sectional curved line group in the horizontal direction” composed of anuncountable number of lines positioned side by side thereon, form a lenssurface as the spine and costae, thus determining a refractive surface.

{circle around (2)}-2: Concave Surface Shape (Spherical or CylindricalSurface) Design

To realize the far vision diopter provided as the input information, aconcave surface shape is designed. The surface becomes a cylindricalsurface if the far vision diopter includes a cylindrical diopter, and aspherical surface if not. In this event, the center thickness CTsuitable for the diopter and the tilt angle between surfaces, the convexsurface and the concave surface, are also designed at the same time,thus determining the shape as a lens. Various conventional knowntechnologies can also be used in the design in this step, and thus thedesign technology of the present invention is unnecessary.

{circle around (3)} Conversion into a Convex Shape of the PresentInvention and Accompanying Rear Surface Correction

In accordance with the far vision diopter and the addition diopter ADDprovided as the input information, the conventional type convexprogressive-power lens is converted into the shape as a lens of thepresent invention.

{circle around (3)}-1: Convex Surface Shape (The Present Invention)Design

In accordance with the far vision diopter and the addition diopter ADDprovided as the input information, the conventional type convexprogressive surface is converted into the convex surface shape of thepresent invention. More specifically, when a surface refractive power inthe horizontal direction and a surface refractive power in the verticaldirection, at a far vision diopter measurement position F1, are DHf andDVf respectively, and a surface refractive power in the horizontaldirection and a surface refractive power in the vertical direction, at anear vision diopter measurement position Ni, are DHn and DVnrespectively, the above-described conventional convex progressive lenssurface (the first refractive surface being the object side surface) isconverted into a refracting surface which satisfies the relationalequations,DHf+DHn<DVf+DVn, and DHn<DVn,or the relational equations,DVn−DVf>ADD/2, and DHn−DHf<ADD/2.In this event, the shape is preferably converted into the convex surfaceshape of the present invention without changing the average surfacerefractive power of the whole convex surface. It is conceivable, forexample, to keep the total average value of the surface refractivepowers in the vertical and horizontal directions in the distance portionand the near portion. The value, however, desirably falls within a rangekeeping a meniscus shape in which the object side surface is convex andthe eyeball side surface is concave.{circle around (3)}-2: Concave Surface Shape (The Present Invention)Design

The amount of transformation in converting from the conventional typeconvex progressive surface into the convex surface shape of the presentinvention in the above-described {circle around (3)}-1, is added to theconcave surface shape designed in {circle around (2)}-2. In other words,the amount of transformation, identical to that of the front surface(the first refractive surface being the object side surface) of the lensadded in the process {circle around (3)}-1, is added to the rear surface(the second refractive surface being the eyeball side surface) of thelens. Note that this transformation is not uniform over the wholesurface though it is similar to “bending” in which the lens itself isbent, but makes a surface which satisfies the relational equationsdescribed in {circle around (3)}-1. It should be noted that the rearsurface corrections are within the scope of the present invention, butare merely corrections of linear approximation, and it is preferable toadd rear surface correction in {circle around (4)}.

{circle around (4)} Rear Surface Correction Accompanying TransmissionDesign, a Listing's Law-Compliant Design, Design for an InnerShift-Compliant Design of a Near Portion, and so on

To realize the optical function provided as the input information, in asituation in which a wearer actually wears a lens, it is desirable tofurther add rear surface correction to the lens of the present inventionobtained in {circle around (3)}.

{circle around (4)}-1: Concave Surface Shape (The Present Invention)Design for Transmission Design

The transmission design means a designing method for obtaining anessential optical function in the situation in which a wearer actuallywears a lens, a designing method of adding a “correction action” foreliminating or reducing occurrence of astigmatism and change in diopterprimarily caused by impossibility of a sight line intersecting at rightangles with a lens surface.

Specifically, as described above, the difference of optical performanceof the lens with respect to a target essential optical performance isgrasped through accurate ray tracing calculation in accordance with thedirection of the sight line, and surface correction to cancel thedifference is implemented. By repeating this, the difference can beminimized to obtain an optimal solution. Generally, it is often verydifficult and actually impossible to directly calculate a lens shapehaving a target optical performance. This is because a “lens shapehaving an arbitrarily set optical performance” does not always actuallyexist. Conversely, it is relatively easy to obtain an “opticalperformance of an arbitrarily set lens shape.” Therefore, it is possibleto bring the optical performance to a target optical performance byfirst provisionally calculating a linearly approximated surface by anarbitrary method, finely adjusting the design parameters in accordancewith evaluation results on the optical performance of the lens shapeusing the approximated surface to sequentially modulate the lens shape,and returning to the evaluation step for a repeat of reevaluation andreadjustment. This technique is one of well-known techniques called“optimization.”

{circle around (4)}-2: Concave Surface Shape (The Present Invention)Design for a Listing's Law-Compliant Design

It is known that three-dimensional rotating motions of eyes when we lookaround are based on a rule called “Listing's law.” When a prescriptiondiopter includes a cylindrical diopter, cylindrical axes of a spectaclelens and the eye may not match to each other in peripheral vision evenif the cylindrical axis of the lens is matched to the “cylindrical axisof the eye in front vision.” It is also possible to add a “correctionaction” for eliminating or reducing occurrence of astigmatism and changein diopter caused by such a mismatch between the cylindrical axes of thelens and the eye in the peripheral vision, to a curved surface being thesurface on the side having a cylindrical correction action of a lensaccording to the present invention.

Specifically, similarly to the method of the “optimization” used in{circle around (4)}-1, the difference of optical performance of the lenswith respect to a target essential optical performance is graspedthrough accurate ray tracing calculation in accordance with thedirection of the sight line, and surface correction to cancel thedifference is implemented. By repeating this, the difference can beminimized to obtain an optimal solution.

{circle around (4)}-3: Concave Surface Shape (The Present Invention)Design for an Inner Shift-Compliant Design of a Near Portion

Though the present invention is of a surface configuration being abi-aspherical surface, both surfaces are not always processed afteracceptance of an order to obtain an effect of the present invention. Itis advantageous in terms of cost and processing speed, for example, toprepare in advance “semifinished products” of the object side surfacemeeting the object of the present invention, select, after acceptance ofan order, from among them a “semifinished product” of the object sidesurface meeting the purpose such as a prescription diopter or theabove-described custom-made product (individual design), and process andfinish only the eyeball side surface after the acceptance of the order.

In a specific example of this method, the object side surface isprepared in advance as a bilaterally symmetrical “semifinished product”in the above-described convex surface shape (the present invention)design in {circle around (3)}-1, and the eyeball side surface isdesigned as a bilaterally asymmetrical curved surface meeting thepurpose after being inputted individual information such as aninter-pupil distance, object distance in near vision, whereby the innershift of the near portion in response to the individual information canbe performed.

Hereinafter, examples of the bi-aspherical surface progressiverefractive lens designed by the above-described designing method will bedescribed with reference to the drawings. FIG. 7 is a view collectivelyshowing in Table 1-1 and Table 1-2 “surface refractive powers” and“results of accurate magnification calculations in a direction of aspecific sight line” of Examples 1, 4, 5, and 6 and Prior arts A, B, andC corresponding to the diopters of Examples 1, 4, 5, and 6. FIG. 8 is aview collectively showing in Table 2-1 and Table 2-2 “surface refractivepowers” and “results of accurate magnification calculations in adirection of a specific sight line” of Examples 2 and 7 and Prior artsA, B, and C corresponding to the diopters of Examples 2 and 7. FIG. 9 isa view collectively showing in Table 3-1 and Table 3-2 “surfacerefractive powers” and “results of accurate magnification calculationsin a direction of a specific sight line” of Example 3 and Prior arts A,B, and C corresponding to the diopters of the example 3. FIG. 10 is aview showing Graphs 1-1, 1-2, 2-1, and 2-2 representing the surfacerefractive power distributions of Example 1 and Example 2, FIG. 11 is aview showing Graphs 3-1 and 3-2 representing the surface refractivepower distributions of Example 3, FIG. 12 is a view showing Graphs 4-1,4-2, 5-1, 5-2, 6-1 and 6-2 representing the surface refractive powerdistributions of Example 4 to Example 6, FIG. 13 is a view showingGraphs 7-1 and 7-2 representing the surface refractive powerdistributions of Example 7, and FIG. 14 is a view showing Graphs A-1,A-2, B-1, B-2, C-1 and C-2 representing the surface refractive powerdistributions of Prior art examples A, B, and C.

FIG. 15 is a view showing Graph 1-3-Msv representing the results,obtained by performing accurate magnification calculations, ofmagnification distributions when lenses of Example 1 and three kinds ofPrior art examples A, B, and C corresponding to the diopters of Example1 are viewed along main gazing lines, FIG. 16 is a view showing Graph1-3-Msh representing results, obtained by performing accuratemagnification calculations, of the magnification distributions when thelenses of Example 1 and the three kinds of Prior art examples A, B, andC corresponding to the diopters of Example 1 are viewed along the maingazing lines, FIG. 17 is a view showing Graph 1-3-Mpv representingresults, obtained by performing accurate magnification calculations, ofthe magnification distributions when the lenses of Example 1 and thethree kinds of Prior art examples A, B, and C corresponding to thediopters of Example 1 are viewed along the main gazing lines, FIG. 18 isa view showing Graph 1-3-Mph representing results, obtained byperforming accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 1 areviewed along the main gazing lines, FIG. 19 is a view showing Graph1-3-M γ v representing results, obtained by performing accuratemagnification calculations, of the magnification distributions when thelenses of Example 1 and the three kinds of Prior art examples A, B, andC corresponding to the diopters of Example 1 are viewed along the maingazing lines, FIG. 20 is a view showing Graph 1-3-M γ h representingresults, obtained by performing accurate magnification calculations, ofthe magnification distributions when the lenses of Example 1 and thethree kinds of Prior art examples A, B, and C corresponding to thediopters of Example 1 are viewed along the main gazing lines, FIG. 21 isa view showing Graph 1-3-SMv representing results, obtained byperforming accurate magnification calculations, of the magnificationdistributions when the lenses of Example 1 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 1 areviewed along the main gazing lines, and FIG. 22 is a view showing Graph1-3-SMh-representing results, obtained by performing accuratemagnification calculations, of the magnification distributions when thelenses of Example 1 and the three kinds of Prior art examples A, B, andC corresponding to the diopters of Example 1 are viewed along the maingazing lines.

FIG. 23 is a view showing Graph 2-3-Msv representing results, obtainedby performing accurate magnification calculations, of magnificationdistributions when lenses of Example 2 and three kinds of Prior artexamples A, B, and C corresponding to the diopters of Example 2 areviewed along main gazing lines, FIG. 24 is a view showing Graph 2-3-Mshrepresenting results, obtained by performing accurate magnificationcalculations, of the magnification distributions when the lenses ofExample 2 and the three kinds of Prior art examples A, B, and Ccorresponding to the diopters of Example 2 are viewed along the maingazing lines, FIG. 25 is a view showing Graph 2-3-Mpv representingresults, obtained by performing accurate magnification calculations, ofthe magnification distributions when the lenses of Example 2 and thethree kinds of Prior art examples A, B, and C corresponding to thediopters of Example 2 are viewed along the main gazing lines, FIG. 26 isa view showing Graph 2-3-Mph representing results, obtained byperforming accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines, FIG. 27 is a view showing Graph2-3-M γ v representing results, obtained by performing accuratemagnification calculations, of the magnification distributions when thelenses of Example 2 and the three kinds of Prior art examples A, B, andC corresponding to the diopters of Example 2 are viewed along-the maingazing lines, FIG. 28 is a view showing Graph 2-3-M γ h representingresults, obtained by performing accurate magnification calculations, ofthe magnification distributions when the lenses of Example 2 and thethree kinds of Prior art examples A, B, and C corresponding to thediopters of Example 2 are viewed along the main gazing lines, FIG. 29 isa view showing Graph 2-3-SMv representing results, obtained byperforming accurate magnification calculations, of the magnificationdistributions when the lenses of Example 2 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 2 areviewed along the main gazing lines, and FIG. 30 is a view showing Graph2-3-SMh representing results, obtained by performing accuratemagnification calculations, of the magnification distributions when thelenses of Example 2 and the three kinds of Prior art examples A, B, andC corresponding to the diopters of Example 2 are viewed along the maingazing lines.

FIG. 31 is a view showing Graph 3-3-Msv representing results, obtainedby performing accurate magnification calculations, of magnificationdistributions when lenses of Example 3 and three kinds of Prior artexamples A, B, and C corresponding to the diopters of Example 3 areviewed along main gazing lines, FIG. 32 is a view showing Graph 3-3-Mshrepresenting results, obtained by performing accurate magnificationcalculations, of the magnification distributions when the lenses ofExample 3 and the three kinds of Prior art examples A, B, and Ccorresponding to the diopters of Example 3 are viewed along the maingazing lines, FIG. 33 is a view showing Graph 3-3-Mpv representingresults, obtained by performing accurate magnification calculations, ofthe magnification distributions when the lenses of Example 3 and thethree kinds of Prior art examples A, B, and C corresponding to thediopters of Example 3 are viewed along the main gazing lines, FIG. 34 isa view showing Graph 3-3-Mph representing results, obtained byperforming accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines, FIG. 35 is a view showing Graph3-3-M γ v representing results, obtained by performing accuratemagnification calculations, of the magnification distributions when thelenses of Example 3 and the three kinds of Prior art examples A, B, andC corresponding to the diopters of Example 3 are viewed along the maingazing lines, FIG. 36 is a view showing Graph 3-3-M γ h representingresults, obtained by performing accurate magnification calculations, ofthe magnification distributions when the lenses of Example 3 and thethree kinds of Prior art examples A, B, and C corresponding to thediopters of Example 3 are viewed along the main gazing lines, FIG. 37 isa view showing Graph 3-3-SMv representing results, obtained byperforming accurate magnification calculations, of the magnificationdistributions when the lenses of Example 3 and the three kinds of Priorart examples A, B, and C corresponding to the diopters of Example 3 areviewed along the main gazing lines, and FIG. 38 is a view showing Graph3-3-SMh representing results, obtained by performing accuratemagnification calculations, of the magnification distributions when thelenses of Example 3 and the three kinds of Prior art examples A, B, andC corresponding to the diopters of Example 3 are viewed along the maingazing lines.

EXAMPLE 1

Table 1-1 in FIG. 7 is a list regarding the surface refractive powers ofExample 1 according to the present invention. The diopters of Example 1correspond to S being 0.00 and ADD being 3.00, with three kinds of priorart examples having the same diopters being listed together forcomparison. It should be noted that Prior art example A, Prior artexample B, and Prior art example C correspond to a “convex surfaceprogressive-power lens” in which the object side surface is aprogressive surface, a “bi-surface progressive-power lens” in which boththe object side surface and eyeball side surface are progressivesurfaces, and a “concave surface progressive-power lens” in which theeyeball side surface is a progressive surface, respectively. Meanings ofitems used in Table 1-1 are as follows:

DVf1: surface refractive power in the vertical direction at a far visiondiopter measurement position F1 on the object side surface,

DHf1: surface refractive power in the horizontal direction at the farvision diopter measurement position F1 on the object side surface,

DVn1: surface refractive power in the vertical direction at a nearvision diopter measurement position N1 on the object side surface,

DHn1: surface refractive power in the horizontal direction at the nearvision diopter measurement position N1 on the object side surface,

DVf2: surface refractive power in the vertical direction at a far visiondiopter measurement position F2 on the eyeball side surface,

DHf2: surface refractive power in the horizontal direction at the farvision diopter measurement position F2 on the eyeball side surface,

DVn2: surface refractive power in the vertical direction at a nearvision diopter measurement position N2 on the eyeball side surface, and

DHn2: surface refractive power in the horizontal direction at the nearvision diopter measurement position N2 on the eyeball side surface.

Graphs 1-1 and 1-2 in FIG. 10 are graphs showing the surface refractivepower distributions along the main gazing lines of Example 1, with thehorizontal axis indicating the lens upper side on the right hand sideand the lens lower side on the left hand side, and the vertical axisindicating the surface refractive power. Here, Graph 1-1 corresponds tothe object side surface, and Graph 1-2 corresponds to the eyeball sidesurface. Besides, the graph shown by a solid line represents the surfacerefractive power distribution in the vertical direction along the maingazing line, and the graph shown by a dotted line represents the surfacerefractive power distribution in the horizontal direction along the maingazing line. In Graphs 1-1, as shown in the drawing, Graph CV1 (solidline) showing the surface refractive power distribution in the verticaldirection along the main gazing line on the object side surface changesin refractive power distribution from the progressive zone portion tothe near portion, while Graph CH1 (dotted line) showing the surfacerefractive power distribution in the horizontal direction has no change.Further, Graph CV1 (solid line) showing the surface refractive powerdistribution in the vertical direction is different from Graph CH1(dotted line) showing the surface refractive power distribution in thehorizontal direction, in the surface refractive power from theprogressive zone portion to the near portion. In this case, astigmatismoccurs in a ray optically passed over the main gazing line on the objectside surface, by about the difference in the surface refractive powerbetween the vertical direction and the horizontal direction. On theother hand, In Graphs 1-2, as shown in the drawing, Graph CV2 (solidline) showing the surface refractive power distribution in the verticaldirection alone the main gazing line on the eyeball side surface doesnot change in refractive power distribution from the distance portionthrough the progressive zone portion to the near portion. On the otherhand, Graph CH2 (dotted line) showing the surface refractive powerdistribution in the horizontal direction varies in refractive powerdistribution from the progressive zone portion to the near portion.Further, Graph CV2 (solid line) showing the surface refractive powerdistribution in the vertical direction is also different, as in Graph1-1, from Graph CH2 (dotted line) showing the surface refractive powerdistribution in the horizontal direction, in the surface refractivepower from the progressive zone portion to the near portion. However,the distribution of the difference in the surface refractive powercorresponds to that in Graph 1-1 in a countertendency, as seen in Graph1-2. which shows that the difference in the surface refractive power isgiven to the ray optically passed over the main gazing line on theeyeball side surface to cancel the astigmatism occurring on the objectside surface. As a result of this, the refractive surfaces of the objectside surface and the eyeball side surface can together provide a farvision diopter and an addition diopter based on prescription values. Itshould be noted that these are graphs for explaining the basicdifference in surface configuration, omitting a case of asphericalprocessing for eliminating astigmatism in a peripheral portion and acase of addition of a cylindrical component for coping with acylindrical diopter.

Further, for comparison, Graphs A-1 and A-2, Graphs B-1 and B-2, andGraphs C-1 and C-2 are shown in FIG. 14 as graphs showing the surfacerefractive power distributions along the main gazing lines of the threekinds of prior art examples having the same diopters, which are listedin Table 1-1. Note that, meanings of terms in these graphs are asfollows:

F1: far vision diopter measurement position on the object side surface,

F2: far vision diopter measurement position on the eyeball side surface,

N1: near vision diopter measurement position on the object side surface,

N2: near vision diopter measurement position on the eyeball sidesurface,

CV1: graph showing the surface refractive power distribution in thevertical direction along the main gazing line on the object side surface(shown by the solid line),

CH1: graph showing the surface refractive power distribution in thehorizontal direction along the main gazing line on the object sidesurface (shown by the dotted line),

CV2: graph showing the surface refractive power distribution in thevertical direction along the main gazing line on the eyeball sidesurface (shown by the solid line), and

CH2: graph showing the surface refractive power distribution in thehorizontal direction along the main gazing line on the eyeball sidesurface (shown by the dotted line).

The surface refractive powers at F1, N1, F2, and N2 on these graphscorrespond to those in the aforementioned Table 1-1, and meanings of theterms such as DVf1 to DHn2 are also the same as those in theaforementioned Table 1-1. Note that one-dotted chain lines in thehorizontal direction at the middle in these graphs show average surfacerefractive powers on the object side surface (total average values ofthe vertical and horizontal surface refractive powers at F1 and N1). Anyof the average surface refractive powers on the object side surface inExample 1 according to the present invention and the three kinds ofprior art examples was uniformly set to 5.50 diopter for fairness incomparison.

The next eight kinds of graphs starting with Graph 1-3-shown in FIG. 15to FIG. 22 are graphs showing results, obtained by performing theabove-described accurate magnification calculations, of magnificationdistributions when the lens of Example 1 according to the presentinvention is viewed along the main gazing line, with the horizontal axisindicating the lens upper side on the right hand side and the lens leftlower side on the left hand side, and the vertical axis indicating themagnification. In the drawing, a thick solid line is for Example 1, athin chain line is for Prior art example A, a thick chain line is forPrior art example B, and a thin solid line is for Prior art example C.These apply to the following graphs of this kind. Note that thehorizontal axis was set to allow comparison for each sight linedirection through use of eyeball rotating angles, and magnificationscales on the vertical axes of the graphs were matched to each other forfairness. Symbols appended to “Graph 1-3-” mean,

Msv: shape factor in the vertical direction,

Msh: shape factor in the horizontal direction,

Mpv: power factor in the vertical direction,

Mph: power factor in the horizontal direction,

M γ v: prism factor in the vertical direction,

M γ h: prism factor in the horizontal direction,

SMv: magnification in the vertical direction, and

SMh: magnification in the horizontal direction,

and, as described above, the magnification SMv in the vertical directionand the magnification SMh in the horizontal direction are in therelation such thatSMv=Msv×Mpv×MγvSMh=Msh×Mph×Mγh.

It should be noted that any of Example 1 and the above-described threekinds of prior art examples was made under specifications with therefractive index n=1.699, the center thickness t=3.0 mm, and no prism atthe geometrical center GC. The objective power (inverse number of theobject distance) was set such that the objective power Px at F1, F2 wasset as Px=0.00 diopter (infinite far), the objective power Px at N1, N2was set as Px=2.50 diopter (40 cm), and the objective powers given inother positions were made by multiplying ratios of the additionalrefractive powers along the main gazing line by 2.50 diopter. Besides,the distance L from the lens rear vertex to the corneal vertex was setas L=15.0 mm, and the distance from the corneal vertex to the eyeballtuning center CR was set as CR=13.0 mm. The eyeball rotating angle θ wasindicated, with the eyeball tuning center point C being positioned onthe normal line passing through the geometrical center GC on the objectside lens surface, the rotating angle when the normal line and the sightline match to each other being regarded as 0 degree, and the upperportion shown with (+) and the lower portion shown with (−). Thereafter,standardization was made such that the eyeball rotating angle θ withrespect to F1, F2 was +15 degrees, and the eyeball rotating angle θ withrespect to N1, N2 was −30.0 degrees, for consideration of allowingcomparison on the same condition even the progressive action and thesurface refractive power distribution were either on front or rear side.

Table 1-2 in FIG. 7 is a list of results obtained by performing theabove-described accurate magnification calculations for a specific sightline direction of Example 1 according to the present invention and thethree kinds of prior art examples prepared for comparison, andcorresponds to the above-described Graph 1-3-SMv (total magnification inthe vertical direction) in FIG. 21 and Graph 1-3-SMh (totalmagnification in the horizontal direction) in FIG. 22. Sincemagnification values are different between the vertical direction andhorizontal direction as described above, both magnifications werecalculated. Here, meanings represented by symbols in Table 1-2 are asfollows:

SMvf: magnification in the vertical direction on a sight line passingthrough a far vision measurement point,

SMvn: magnification in the vertical direction on a sight line passingthrough a near vision measurement point,

SMvfn: magnification difference in the vertical direction (SMvn−SMvf),

SMhf: magnification in the horizontal direction on a sight line passingthrough a far vision measurement point,

SMhn: magnification in the horizontal direction on a sight line passingthrough a near vision measurement point, and

SMhfn: magnification difference in the horizontal direction (SMhn−SMhf).

SMvfn and SMhfn in Table 1-2, that is, the magnification difference inthe vertical direction (SMvn−SMvf) and the magnification difference inthe horizontal direction (SMhn−SMhf), show that the values ofmagnification differences of Example 1 according to the presentinvention are suppressed to as low as 0.1342 and 0.0954, whereas thoseof the prior art examples are 0.1380 and 0.1015 in A, 0.1360 and 0.0988in B, and 0.1342 and 0.0961 in C. In other words, the magnificationdifference between the distance portion and the near portion of Example1 according to the present invention are made further smaller than thoseof Prior art 1, which shows that Example 1 is improved more greatly thanPrior art 1 also in distortion and sway of an image. Note that thedifference between the vertical direction and the horizontal directionin calculating the magnification is not taken into consideration at allin the patent specification corresponding to the above-described Priorart 1. However, as is immediately apparent from comparison between Graph1-3-SMv (total magnification in the vertical direction) in FIG. 21 andGraph 1-3-SMh in FIG. 22 (total magnification in the horizontaldirection) resulting from accurate magnification calculations,corresponding to Example 1 according to the present invention,magnification distributions of an image in the vertical direction andthe horizontal direction are apparently different. Further, it is easilyread that this difference is prominent mainly in the near portion and aportion lower than that (at an eyeball rotating angle of around −20degrees and lower).

As expressed in the above-described magnification calculation equations,the magnification in the vertical direction SMv=Msv×Mpv×Mγv,the magnification in the horizontal direction SMh=Msh×Mph×Mγh,Graph 1-3-SMv is obtained by multiplying three elements, that is, valuesof Graph 1-3-Msv, Graph 1-3-Mpv, and Graph 1-3-M γ v, and similarlyGraph 1-3-SMh is obtained by multiplying three elements, that is, valuesof Graph 1-3-Msh, Graph 1-3-Mph, and Graph 1-3-M γ h. In comparisonbetween the elements in the vertical direction and the horizontaldirection here, there is no apparent difference found between Msv andMsh which are shape factors, whereas there is a difference found betweenMpv and Mph in a portion lower than the near portion (at an eyeballrotating angle of around −25 degrees and lower). Further, there is anobvious difference between M γ v and M γ h in the near portion and alower portion than that (at an eyeball rotating angle of around −15degrees and lower). In short, it is shown that the major cause of thedifference between Graph 1-3-SMv and Graph 1-3-SMh is the differencebetween M γ v and M γ h, the secondary cause thereof is the differencebetween Mpv and Mph, and there is no obvious difference found betweenMsv and Msh, which are almost irrelevant thereto. Consequently, thereason why there is no difference found between magnifications in thevertical direction and the horizontal direction in the patentspecification corresponding to Prior art 1 is that the prism factors M γv and M γ h, which are maj or causes of a magnification difference, arenot taken into consideration at all, and because the object distance andthe angle between the sight line and lens are neglected, there is nodifference found between the power factors Mpv and Mph, which aresecondary causes. Further, there is no difference found among theexamples in the magnification difference between the distance portionand the near portion, as long as in the scale used in Example 1 of thepresent invention, in the shape factors Msv and Msh which are regardedas reasons of improvement in Prior art 1.

In Prior art 1 “the distortion and sway of an image can be reduced” by“decreasing the magnification difference between the distance portionand the near portion,” and further “decreasing the magnificationdifference between the vertical direction and the horizontal direction”is also regarded as having an effect of “capable of reducing thedistortion and sway of an image” in the present invention. This isintended to prevent a square item from looking flat, or a circular itemfrom looking oval. The improvement in visual sense would be essentiallyseen as “bringing the ratio closer to 1” rather than “reducing thedifference.” What is important here is that the sense of a square itemlooking flat or a circular item looking oval is not due to a “far-nearratio” but due to a “vertical-horizontal ratio.” In other words, thepresent invention can provide an improved effect of “capable of reducingthe distortion and sway of an image” not only by “decreasing themagnification difference between the distance portion and the nearportion” but also by “decreasing the magnification difference betweenthe vertical direction and the horizontal direction to bring themagnification ratio closer to 1.” These tendencies are prominent mainlyin a portion lower than the near portion (at an eyeball rotating angleof around −25 degrees and lower).

EXAMPLE 2

Table 2-1 in FIG. 8 is a list regarding the surface refractive powers ofExample 2 according to the present invention. The diopters of Example 2correspond to S being +6.00 and ADD being 3.00, with three kinds ofprior art examples having the same diopters being listed together forcomparison. It should be noted that Prior art example A, Prior artexample B, and Prior art example C correspond to a “convex surfaceprogressive-power lens” in which the object side surface is aprogressive surface, a “bi-surface progressive-power lens” in which boththe object side surface and eyeball side surface are progressivesurfaces, and a “concave surface progressive-power lens in which theeyeball side surface is a progressive surface, respectively. Meanings ofterms such as DVf1 to DHn2 used in Table 2-1 are the same as those inthe above-described Table 1-1. Graphs 2-1 and 2-2 are graphs showing thesurface refractive power distributions along the main gazing lines ofExample 2 according to the present invention, with the horizontal axisindicating the lens upper side on the right hand side and the lens lowerside on the left hand side, and the vertical axis indicating the surfacerefractive power. Here, Graph 2-1 corresponds to the object sidesurface, and Graph 2-2 corresponds to the eyeball side surface. Besides,the graph shown by a solid line represents the surface refractive powerdistribution in the vertical direction along the main gazing line, andthe graph shown by a dotted line represents the surface refractive powerdistribution in the horizontal direction along the main gazing line. Itshould be noted that these are graphs for explaining the basicdifference in surface configuration, omitting a case of asphericalprocessing for eliminating astigmatism in a peripheral portion and acase of addition of a cylindrical component for coping with acylindrical diopter.

Further, Graphs A-1 and A-2, Graphs B-1 and B-2, and Graphs C-1 and C-2which are used in the above-described Example 1 are used again as graphsshowing the surface refractive power distributions along the main gazinglines of the three kinds of prior art examples having the same diopters,which are listed in Table 2-1 for comparison. Therefore, meaning ofterms in these graphs are the same as those in the above-describedExample 1. The surface refractive powers at F1, N1, F2, and N2 shouldcorrespond to those in Table 2-1, and any of the average surfacerefractive powers on the object side surfaces shown by one-dotted chainlines in the horizontal direction at the middle should have a deep curveof 10.50 diopter on the ground of correspondence to Table 2-1. In Graphs2-1 and Graph 2-2 of FIG. 10. Graph CV1 (solid line) showing the surfacerefractive power distribution in the vertical direction along the maingazing line on the object side surface. Graph CH1 (dotted line) showingthe surface refractive power distribution in the horizontal direction.Graph CV2 (solid line) showing the surface refractive power distributionin the vertical direction along the main gazing line on the eyeball sidesurface, and Graph CH2 (dotted line) showing the surface refractivepower distribution in the horizontal direction have appearances ofchange from the distance portion through the progressive zone portion tothe near portion showing similar tendencies as those in Example 1. Thisshows that the difference in the surface refractive power is given tothe ray passed over the main gazing line on the eyeball side surface tocancel the astigmatism occurrina on the object side surface. As a resultof this. the refractive surfaces of the object side surface and theeyeball side surface can also together provide a far vision diopter andan addition diopter based on prescription values in Example 2 as inExample 1.

The next eight kinds of graphs starting with Graph 2-3-shown in FIG. 23to FIG. 30 are graphs showing results, obtained by performing theabove-described accurate magnification calculations, of magnificationdistributions when the lens of Example 2 according to the presentinvention is viewed along the main gazing line. Meanings of terms andsymbols appended to “Graph 2-3-” are the same as those in theabove-described Example 1 other than that thick lines in the drawingsare for Example 2. Although any of the refractive indexes, objectivepowers, and eyeball rotating angles used in Example 2 and theabove-described three kinds of prior art examples was the same as thatin the above-described Example 1, only the center thickness t was set at6.0 mm close to an actual product because Example 2 and theabove-described three kinds of prior art examples have diopters of Sbeing +6.00 and ADD being 3.00.

Table 2-2 in FIG. 8 is a list of results obtained by performing accuratemagnification calculations for a specific sight line direction ofExample 2 according to the present invention and three kinds of priorart examples prepared for comparison, and corresponds to theabove-described Graph 2-3-SMv (total magnification in the verticaldirection) and Graph 2-3-SMh (total magnification in the horizontaldirection). Here, meanings represented by symbols in Table 2-2 are thesame as those in the above-described Table 1-2.

SMvfn and SMhfn in Table 2-2, that is, the magnification difference inthe vertical direction (SMvn−SMvf) and the magnification difference inthe horizontal direction (SMhn−SMhf), show that the values ofmagnification differences of Example 2 according to the presentinvention are suppressed to as low as 0.2151 and 0.1199, whereas thoseof the prior art examples are 0.2275 and 0.1325 in A, 0.2277 and 0.1268in B, and 0.2280 and 0.1210 in C. In other words, the magnificationdifference between the distance portion and the near portion of Example2 according to the present invention are made further smaller than thoseof Prior art 1, which shows that Example 2 is improved more greatly thanPrior art 1 also in distortion and sway of an image. As is immediatelyapparent, as in Example 1, from comparison between Graph 2-3-SMv (totalmagnification in the vertical direction) and Graph 2-3-SMh (totalmagnification in the horizontal direction) resulting from accuratemagnification calculations, corresponding to Example 2 according to thepresent invention, magnification distributions of an image in thevertical direction and the horizontal direction are apparentlydifferent.

Further, it is easily read that this difference is prominent mainly in aportion lower than the middle portion (at an eyeball rotating angle ofaround −10 degrees and lower). As in Example 1, Graph 2-3-SMv isobtained also in Example 2 by multiplying three elements, that is,values of Graph 2-3-Msv, Graph 2-3-Mpv, and Graph 2-3-M γ v, andsimilarly Graph 2-3-SMh is obtained by multiplying three elements, thatis, values of Graph 2-3-Msh, Graph 2-3-Mph, and Graph 2-3-M γ h. Here,in comparison between the elements in the vertical direction and thehorizontal direction, there is no apparent difference found between Msvand Msh which are shape factors, whereas there is a difference foundbetween Mpv and Mph in a portion lower than the near portion (at aneyeball rotating angle of around 20 degrees and lower). Further, thereis an obvious difference between M γ v and M γ h in a portion lower thanthe middle portion (at an eyeball rotating angle of around −10 degreesand lower). There is also a difference found in an upper portion of thedistance portion (at an eyeball rotating angle of around +20 degrees andupper), which is negligible because a difference existing between theexamples in a quite upper portion of the distance portion (at an eyeballrotating angle of around +30 degrees and upper) with less frequent use.

In short, it is shown, as in the above-described Example 1, that themajor cause of the difference between Graph 2-3-SMv in FIG. 29 and Graph2-3-SMh in FIG. 30 is the difference between M γ v and M γ h, thesecondary cause thereof is the difference between Mpv and Mph, and thereis no obvious difference found between Msv and Msh, which are almostirrelevant thereto. Further, there is no difference found among theexamples in the magnification difference between the distance and nearportions, as long as in the scale used in Example 2 of the presentinvention, in the shape factors Msv and Msh, which are regarded asreasons of improvement in Prior art 1. Note that, as in Example 1, thepresent invention can provide, also in Example 2, an improved effect of“capable of reducing the distortion and sway” not only by “decreasingthe magnification difference between the distance portion and the nearportion” but also by “decreasing the magnification difference betweenthe vertical direction and the horizontal direction to bring themagnification ratio closer to 1.” These tendencies are prominent mainlyin a portion lower than the near portion (at an eyeball rotating angleof around −25 degrees and lower).

EXAMPLE 3

Table 3-1 in FIG. 9 is a list regarding the surface refractive powers ofExample 3 according to the present invention. The diopters of Example 3correspond to S being −6.00 and ADD being 3.00, with three kinds ofprior art examples having the same diopters being listed together forcomparison. It should be noted that Prior art example A, Prior artexample B, and Prior art example C correspond to a “convex surfaceprogressive-power lens” in which the object side surface is aprogressive surface, a “bi-surface progressive power lens” in which boththe object side surface and eyeball side surface are progressivesurfaces, and a “concave surface progressive-power lens in which theeyeball side surface is a progressive surface, respectively. Meanings ofterms such as DVf1 to DHn2 used in Table 3-1 are the same as those inthe above-described Table 1-1 and Table 2-1.

Graphs 3-1 and 3-2 in FIG. 11 are graphs showing the surface refractivepower distributions along the main gazing lines of Example 3 accordingto the present invention, with the horizontal axis indicating the lensupper side on the right hand side and the lens lower side on the lefthand side, and the vertical axis indicating the surface refractivepower. Here, Graph 3-1 corresponds to the object side surface, and Graph3-2 corresponds to the eyeball side surface. Besides, the graph shown bya solid line represents the surface refractive power distribution in thevertical direction along the main gazing line, and the graph shown by adotted line represents the surface refractive power distribution in thehorizontal direction along the main gazing line. It should be noted thatthese are graphs for explaining the basic difference in surfaceconfiguration, omitting a case of aspherical processing for eliminatingastigmatism in a peripheral portion and a case of addition of acylindrical component for coping with a cylindrical diopter.

Further, Graphs A-1 and A-2, Graphs B-1 and B-2, and Graphs C-1 and C-2which are used in the above-described Examples 1 and 2 are used again asgraphs showing the surface refractive power distributions along the maingazing lines of the three kinds of prior art examples having the samediopters, which are listed in Table 3-1 in FIG. 9 for comparison.Therefore meaning of terms in these graphs are the same as those in theabove-described Examples 1 and 2. The surface refractive powers at F1,N1, F2, and N2 should correspond to those in the aforementioned Table3-1, and any of the average surface refractive powers on the object sidesurface shown by one-dotted chain lines in the horizontal direction atthe middle should have a shallow curve with 2.50 diopter for the groundof correspondence to Table 3-1. In Graphs 3-1 and Granh 3-2 of FIG. 12,Graph CVI (solid line) showing the surface refractive power distributionin the vertical direction along the main gazing line on the object sidesurface, Gravh CH1 (dotted line) showing the surface refractive powerdistribution in the horizontal direction. Graph CV2 (solid line) showingthe surface refractive power distribution in the vertical directionalong the main gazing line on the eyeball side surface, and Graph CH2(dotted line) showing the surface refractive power distribution in thehorizontal direction have appearances of change from the distanceportion through the progressive zone portion to the near portion showingsimilar tendencies as those in Example 1 and Example 2, which shows thatthe difference in the surface refractive power is given to the raypassed over the main gazing line on the eyeball side surface to cancelthe astigmatism occurring on the object side surface. As a result ofthis, the refractive surfaces of the object side surface and the eyeballside surface can together provide a far vision diopter and an additiondiopter based on prescription values as in Example 1 and Example 2.

The next eight kinds of graphs starting with Graph 3-3-shown in FIG. 31to FIG. 38 are graphs showing results, obtained by performing theabove-described accurate magnification calculations, of magnificationdistributions when the lens of Example 3 according to the presentinvention is viewed along the main gazing line. Meanings of terms andsymbols appended to “Graph 3-3-” are the same as those in theabove-described Examples 1 and 2 other than that thick lines in thedrawings are for Example 3. Although any of the refractive indexes,objective powers, and eyeball rotating angles used in Example 3 and theabove-described three kinds of prior art examples was the same as thatin the above-described Examples 1 and 2, only the center thickness t wasset to 1.0 mm close to an actual product because Example 3 and theabove-described three kinds of prior art examples had diopters of Sbeing −6.00 and ADD being 3.00.

Table 3-2 in FIG. 9 is a list of results obtained by performing accuratemagnification calculations for a specific sight line direction ofExample 3 according to the present invention and three kinds of priorart examples prepared for comparison, and corresponds to theabove-described Graph 3-3-SMv (total magnification in the verticaldirection) and Graph 3-3-SMh (total magnification in the horizontaldirection). Here, meanings represented by symbols in Table 3-2 are thesame as those the meanings in the above-described Table 1-2 and Table2-2.

SMvfn and SMhfn in Table 3-2, that is, the magnification difference inthe vertical direction (SMvn−SMvf) and the magnification difference inthe horizontal direction (SMhn−SMhf), show that the values ofmagnification differences of Example 3 according to the presentinvention are at 0.0512 and 0.0726, whereas those of the prior artexamples are 0.0475 and 0.0774 in A, 0.0418 and 0.0750 in B, and 0.0363and 0.0727 in C, showing that in Example 3 the magnification differencein the vertical direction increases, whereas the magnificationdifference in the horizontal direction decreases. However, consideringthe magnification difference in the vertical direction having a lowvalue, which is ⅓ to ⅕ that of the above-described Examples 1 andExample 2, with a slight decrease in the magnification difference in thehorizontal direction, it can be said that there is not so greatmagnification difference between the distance portion and the nearportion of Example 3 according to the present invention as compared tothose of Prior art 1. Meanwhile, a study of Graph 3-3-SMv (totalmagnification in the vertical direction) and Graph 3-3-SMh (totalmagnification in the horizontal direction) obtained by performingaccurate magnification calculations corresponding to Example 3 accordingto the present invention, shows that Example 3 according to the presentinvention, as compared to the prior art examples, has the least“tendency of the magnification in the vertical direction to be smallerthan 1” especially in a portion lower than the near portion (at aneyeball rotating angle of around −20 degrees and lower), which resultsin the least “magnification difference between the vertical directionand the horizontal direction” so that distortion and sway of an imageare improved further than in the prior art examples.

It should be noted that in Graph 3-3-SMv (total magnification in thevertical direction) in FIG. 37, there occurs a significant difference inmagnification distribution of an image between the vertical directionand the horizontal direction mainly in a portion lower than the middleportion (at an eyeball rotating angle of around −10 degrees and lower)and in an upper portion of the distance portion (at an eyeball rotatingangle of around +10 degrees and upper), whereas there occurs adifference among the examples in a portion lower than the near portion(at an eyeball rotating angle of around −20 degrees and lower) and in aslightly upper portion of the distance portion (at an eyeball rotatingangle of around +25 degrees and upper). Of them, the difference in theslightly upper portion of the distance portion is negligible because itis infrequently used, while that in the portion lower than the nearportion is nonnegligible because it is frequently used. As a result, inExample 3 according to the present invention, as compared to the priorart examples, the magnification in the vertical direction is closest to1 especially in the portion lower than the near portion (at an eyeballrotating angle of around −20 degrees and lower), which results in theleast “magnification difference between the vertical direction and thehorizontal direction” so that distortion and sway of an image areimproved further than in the prior art examples. Note that thesetendencies are prominent mainly in the portion lower than the nearportion (at an eyeball rotating angle of around −25 degrees and lower).Further, there is no difference, as in Example 1 and Example 2 of thepresent invention, found among the examples in the magnificationdifference between the distance and near portions even in the scale usedin Example 3, in the shape factors Msv and Msh which are regarded asreasons of improvement in Prior art 1.

EXAMPLES 4 TO 7

As examples of the present invention, there are various possiblecombinations of distributions of surface refractive powers within thescope described in claims other than the above-described Examples 1 to3. Examples 4 to 6 are shown here as applications having the samediopters as Example 1, and Example 7 as an application having the samediopters as Example 2. Lists and graphs of the surface refractive powersand results obtained by performing accurate magnification calculationsfor a specific sight line direction of these examples are shown in Table1-1 and Table 1-2 in FIG. 7 and Graphs 4-1 and 4-2 to Graphs 7-1 and 7-2in FIG. 12 to FIG. 14.

Modifications

Further, in the present invention, it is also possible to meet thedemand for custom-made product (individual design) by incorporating,into the lens design as input information, not only usual prescriptionvalues but also, for example, the distance from the corneal vertex tothe lens rear vertex, the distance from the eyeball rotating center tothe lens rear vertex, the degree of aniseiconia between right and lefteyes, the difference in height between right and left eyes, the objectdistance in near vision most frequently used, the forward tilt angle (inan up-down direction) and horizontal tilt angle (in a right-leftdirection) of a frame, the bevel position in the edge thickness of thelens, and so on, as individual factors of spectacle wearers which havebeen rarely grasped by lens manufactures. Although the present inventionhas a bi-aspherical surface configuration, it is not always necessary toprocess both surfaces after acceptance of an order to obtain the effectof the present invention. It is also advantageous in terms of cost andprocessing speed, for example, to prepare in advance “semifinishedproducts” of the object side surface meeting the object of the presentinvention, select, after acceptance of an order, from among them a“semifinished product” of the object side surface meeting the purposesuch as a prescription diopter or the above-described custom-madeproduct (individual design), and process and finish only the eyeballside surface after acceptance of the order.

As a specific example of this method, for example, previous preparationof a bilaterally symmetrical “semifinished product” of the object sidesurface is conceivable. Then, an inner shift of the near portion inresponse to the convergence action of an eye in near vision can beincorporated by making the eyeball side surface into a bilaterallyasymmetrical curved surface meeting the purpose in accordance withindividual information such as the inter-vertex distance or the objectdistance in the near vision. As a matter of course, there are variousconceivable means for obtaining or defining the individual informationnot only by actual measurement but also by estimation or by setting toaverage or standard values, but the present invention will not belimited to those means. Besides, it is possible to add a “correctionaction” for eliminating or reducing occurrence of astigmatism and changein diopter primarily caused by impossibility of the sight lineintersecting at right angles with the lens surface, to the object sidesurface or the eyeball side surface or both curved surfaces of theobject side surface and the eyeball side surface, in performance ofoptical calculations for incorporating not only usual prescriptionvalues but also the above-described individual factors into the lensdesign.

Further, it is generally known that three-dimensional rotating motionsof eyes when we look around are based on a rule called “Listing's law.”When a prescription diopter includes a cylindrical diopter, cylindricalaxes of a spectacle lens and the eye may not match to each other inperipheral vision even if the cylindrical axis of the lens is matched tothe “cylindrical axis of the eye in front vision.” It is also possibleto add a “correction action” for eliminating or reducing occurrence ofastigmatism and change in diopter caused by such a mismatch between thecylindrical axes of the lens and the eye in peripheral vision, to acurved surface being the surface on the side having a cylindricalcorrection action of a lens according to the present invention.

It should be noted that, as the definition of the “predeterminedaddition diopter” in the present invention, any of the followingdefinitions in various cases can be employed, including a case in whichthe diopter is defined as the difference between refractive powersmeasured by placing an opening of a lens meter at the far vision dioptermeasurement position F1 and at the near vision diopter measurementposition N1 on the object side surface as shown in FIG. 6; and inaddition, a case in which the diopter is defined as the differencebetween refractive powers measured by placing an opening of a lens meterat the far vision diopter measurement position F2 and at the near visiondiopter measurement position N2 on the eyeball side surface; further acase in which the diopter is defined as the difference between arefractive power measured by placing an opening of a lens meter at thefar vision diopter measurement position F2 on the eyeball side surfaceand a refractive power measured at N3 by rotating the opening of thelens meter about the eyeball rotating center position and directing ittoward the near vision diopter measurement position N2; and a case usingonly refractive power component in the horizontal direction for eachrefractive power.

INDUSTRIAL AVAILABILITY

According to the present invention, a progressive action of aprogressive-power lens is divided in the vertical direction and thehorizontal direction of the lens, and then an optimal sharing ratiobetween the front and rear two surfaces on the object side and theeyeball side is set in each direction to configure one bi-asphericaltype progressive-power lens, so that an advantage that the visual filedis widened in the horizontal direction can be received by increasing thesharing ratio of the progressive action in the horizontal direction onthe rear surface (the eyeball side surface) and the disadvantage ofincreasing the eyeball rotating angle between the distance and nearportions in the vertical direction can be restrained by increasing thesharing ratio of the progressive action in the vertical direction on thefront surface (the object side surface).

Further, a wide effective visual field with less distortion in wearingcan he provided in the progressive-power lens by reducing amagnification difference of an image between the distance portion andthe near portion.

Furthermore, it is also possible to use a “bilaterally symmetricalsemifinished product” as the object side surface of theprogressive-power lens and process after acceptance of an order only theeyeball side surface into a bilaterally asymmetrical curved surfacecoping with a convergence action of an eye in near vision, therebyreducing processing time and cost.

1. A bi-aspherical type progressive-power lens with a progressiverefractive power action dividedly allotted to a first refractive surfacebeing an object side surface and a second refractive surface being aneyeball side surface, wherein when on said first refractive surface, asurface refractive power in a horizontal direction and a surfacerefractive power in a vertical direction, at a far vision dioptermeasurement position F1, are DHf and DVf respectively, and on said firstrefractive surface, a surface refractive power in a horizontal directionand a surface refractive power in a vertical direction, at a near visiondiopter measurement position N1, are DHn and DVn respectively,relational equations,DHf+DHn<Dvf+DVn, and DHn<DVn are satisfied, and surface astigmatismcomponents at F1 and N1 of said first refractive surface are cancelledby said second refractive surface so that said first and secondrefractive surfaces together provide a far vision diopter (Df) and anaddition diopter (ADD) based on prescription values.
 2. Thebi-aspherical type progressive-power lens according to claim 1, whereinrelational equations DVn−DVf>ADD/2, and DHn−DHf<ADD/2 are satisfied. 3.The bi-aspherical type progressive-power lens according to claim 2,wherein said first refractive surface is bilaterally symmetrical withrespect to one meridian passing through the far vision dioptermeasurement position F1, said second refractive surface is bilaterallyasymmetrical with respect to one meridian passing through a far visiondiopter measurement position F2 of said second refractive surface, and aposition of a near vision diopter measurement position N2 on said secondrefractive surface is shifted inward to a nose by a predetermineddistance.
 4. The bi-aspherical type progressive-power lens according toclaim 2, wherein said first refractive surface is a rotation surfacewith as a generatrix one meridian passing through the far vision dioptermeasurement position F1, said second refractive surface is bilaterallyasymmetrical with respect to one meridian passing through a far visiondiopter measurement position F2 on said second refractive surface, and aposition of a near vision diopter measurement position N2 on said secondrefractive surface is shifted inward to a nose by a predetermineddistance.
 5. The bi-aspherical type progressive-power lens according toclaim 1, wherein said first refractive surface is bilaterallysymmetrical with respect to one meridian passing through the far visiondiopter measurement position F1, said second refractive surface isbilaterally asymmetrical with respect to one meridian passing through afar vision diopter measurement position F2 of said second refractivesurface, and a position of a near vision diopter measurement position N2on said second refractive surface is shifted inward to a nose by apredetermined distance.
 6. The bi-aspherical type progressive-power lensaccording to claim 5, wherein said first refractive surface is arotation surface with as a generatrix one meridian passing through thefar vision diopter measurement position F1, said second refractivesurface is bilaterally asymmetrical with respect to one meridian passingthrough a far vision diopter measurement position F2 on said secondrefractive surface, and a position of a near vision diopter measurementposition N2 on said second refractive surface is shifted inward to anose by a predetermined distance.
 7. The bi-aspherical typeprogressive-power lens according to claim 1, wherein said firstrefractive surface is a rotation surface with as a generatrix onemeridian passing through the far vision diopter measurement position F1,said second refractive surface is bilaterally asymmetrical with respectto one meridian passing through a far vision diopter measurementposition F2 on said second refractive surface, and a position of a nearvision diopter measurement position N2 on said second refractive surfaceis shifted inward to a nose by a predetermined distance.